1. Field of the Invention
This invention relates to the manufacture of complexly shaped articles such as BLISKs, and, more particularly, to a manufacturing process incorporating an iterative technique to refine tooling design.
2. Description of the Related Art
Some complexly shaped articles are manufactured by techniques which require the development of specially shaped tooling that accomplishes the shaping of the workpiece. In an example of particular interest, an integral compressor blade/disk (BLISK) structure for a gas turbine engine is manufactured as a single integral piece by electrochemical machining (ECM). In ECM, a cathode is positioned adjacent to the workpiece, and an electrical circuit is established with an electrolyte flowing between the cathode and the workpiece. A current flows through the cathode and the workpiece, removing metal from the workpiece and into the electrolyte. The cathode is gradually moved toward the workpiece as the shape of the electrochemically machined workpiece becomes closer to that of the cathode. At the conclusion of the process, the workpiece is shaped similarly to the cathode.
If the workpiece had exactly the shape of the cathode on the first try, there would be no need for any redesign of the cathode. However, because of a number of factors such as the electrical field characteristics, the flow pattern of the electrolyte, and the shape of the workpiece, the first trial for the shape of the final machined article is generally not the same as that of the cathode. A redesign of the cathode is therefore required, followed by a second try at producing the workpiece. In the conventional approach to the redesign, a tabular point technique is used to compare the actual shape of the machined article with the desired shape. The cathode shape is redesigned to produce a closer correspondence between the shape of the next generation of the workpiece and the desired shape. This cathode and surface redesign is not without limitations, however, because the redesign must ensure that a smooth, aerodynamic shape of the final article is achieved.
Experience has shown that, even for experienced manufacturing process designers, the redesign process is extremely tedious and costly. In the case of a BLISK, a total of 15-20 iterations is typically required. That is, it takes 15-20 iterations before the shape of the cathode converges on a final shape that produces the desired shape of the BLISK. Each iteration requires a redesign, manufacture of a new cathode, electrochemical machining of a new BLISK (or at least part of the BLISK), and measurements of the shape of the BLISK. The next cathode is designed to overcome remaining shape differences with the desired shape and avoid changes which would introduce new shape problems. The design of a new BLISK and preparation of the workable ECM tooling typically requires 1-2 months.
Similar problems are encountered with other complexly shaped articles made by ECM and other manufacturing techniques.
There is a need for an improved approach to the manufacturing of complexly shaped articles. The present invention fulfills this need, and further provides related advantages.
The present invention provides a method for producing complexly shaped articles that require redesign of manufacturing tooling. It is particularly useful in the design of a cathode for electrochemical machining. The approach produces results at least as good as those of conventional design techniques, and in some cases superior to those of conventional design techniques. The present methodology requires many fewer design iterations than conventional techniques, typically no more than 3 iterations as compared with 15-20 iterations for conventional procedures. A new complex article and its tooling may be produced in just a few days rather than requiring weeks.
The present method produces a complexly shaped article having a smoothly varying specified shape. The method uses a shaping process that operates with a set of shaping parameters, such as an electrochemical machining process wherein the shaping parameters define the cathode. The method comprises the steps of preparing a trial article having a trial shape using the shaping process, wherein the set of shaping parameters is a set of trial shaping parameters. A set of deviations of the trial shape from the specified shape at a plurality of surface grid points on a surface of the trial article is measured, to find how close the trial article is to the desired specified shape. A set of revised shaping parameters is determined by first defining at least one reshaping routine specific to the shaped article. Each reshaping routine repositions at least one adjacent surface grid point responsive to a repositioning of a repositioned surface grid point. The reshaping routine includes an automatic step of establishing a smoothly varying shape of the surface. The one or more reshaping routines are selected according to commonly required shape changes that are needed during the redesign process.
The designer selects a selected reshaping routine and operates the selected reshaping routine by repositioning a selected surface grid point using the selected reshaping routine. The reshaping routine responsively repositions at least one adjacent surface grid point and establishes a smoothly varying shape of the surface. The steps of selecting and repositioning are repeated, if necessary, for another surface grid point until all grid points on the surface of the trial shape are moved to locations defined by the specified shape. The steps of selecting, repositioning, and repeating produce the set of revised shaping parameters. A reshaped article is prepared using the shaping process with the set of revised shaping parameters from the step of determining. In the preferred case, the cathode of the electrochemical machining process has a shape according to the revised cathode shape parameters.
The present approach is based upon the recognition that the reshaping of the article may best be accomplished by attention to a number of grid points simultaneously rather than a single grid point. As one grid point on the surface is repositioned, adjacent grid points are also repositioned in a self-consistent manner so that the basic smooth surface shape is not compromised by the repositioning of specific grid points so as to be within the tolerance limits. The result is that the reshaping process is accomplished faster and with fewer iterations than heretofore possible.
Other features and advantages of the present invention will be apparent from the following more detailed description of the preferred embodiment, taken in conjunction with the accompanying drawings, which illustrate, by way of example, the principles of the invention. The scope of the invention is not, however, limited to this preferred embodiment.